UV curing intaglio ink

ABSTRACT

An intaglio printing ink comprising a first binder compound selected from the group of water-soluble or water-thinnable acrylate oligomers, and optionally, a second monomeric binder compound selected from the group comprising water-soluble or water-thinnable PEG diacrylate or polyethoxylated polyol triacrylate monomers to adjust the viscosity of the ink composition. To initiate polymerization of the binder compounds upon irradiation by electromagnetic radiation or electron beam radiation a photoinitiator is included. Further optional additives, such as pigments, fillers, photosensitizers, stabilizers emulsifiers and security pigments may be present. The ink shows excellent wipeability and allows precipitation from the wiping solution.

[0001] The invention relates to an intaglio ink composition, a method ofmanufacturing and applying said composition, a use of said compositionin an intaglio printing process and a method of precipitating theresulting wiping solution, as well as a security document realized byintaglio printing using said composition. The said ink compositioncomprises components which are polymerizable via a radical reaction pathby irradiation with electromagnetic or electron beam radiation. The saidink composition additionally exhibits a suitable dispersibility inwiping solutions of low sodium hydroxide concentration.

[0002] The printing of security documents requires an outstandingprinting quality and particular measures to prevent counterfeiting andforgery of the printed documents.

[0003] Security documents are printed preferably by the intaglioprinting process. The term “intaglio printing” as used in thisapplication shall apply to the so-called “engraved steel die” or “copperplate” printing process which is well known to the skilled in the art.The printing plates used herein are usually chromium plated, engravednickel plates or cylinders, made by galvanic replication of an—oftenhand-engraved—original copper plate. The following shall not apply tothe also well known rotogravure or gravure printing processes, whichrely on a different type of ink.

[0004] In engraved steel die rotary printing, a rotating engraved steelcylinder carrying the pattern or image to be printed, is supplied withink by one or more template inking cylinders by which a pattern of inksof different color is transferred to the printing cylinder. Subsequentto inking, any excess of ink on the plain surface of the printingcylinder is wiped off by a rotating wiping cylinder covered by aplastisol. Then, the remaining ink in the engraving of the printingcylinder is transferred under pressure onto the substrate to be printed,which may be paper or plastic material in sheet or web form. The wipingcylinder, in turn, is continuously cleaned using diluted aqueous sodiumhydroxide as an emulsifying medium for the wiped-off excess ink, or apaper/calico wiping device, or an organic solvent such astrichloroethylene. These process steps and the machines used forengraved steel die printing are known to the skilled in the art.

[0005] Printing inks for the printing of security documents by theengraved steel die method on presently used sheet fed or web fedintaglio presses must satisfy to the following requirements:

[0006] correct rheological properties at the moment of ink transfer tothe printing cylinder and at the moment of printing (rheology).

[0007] The ability of the ink to be easily and quantitatively removedfrom the non printing areas of the printing die surface (wipeability).

[0008] The ease of cleaning of the wiping cylinder with an aqueoussolution containing 0.1 to 1% of caustic soda and a similarconcentration of a detergent, or even with pure water (detergeability);

[0009] Stability of the ink before printing, on the inking rollers,until the moment of printing;

[0010] Film forming characteristics such that they allow furthermanipulation of sheets or webs carrying printed films of up to 200microns thickness at latest 24 hours after printing or, preferably,immediately after printing;

[0011] Non-offsetting properties: In the case of printing on continuousweb at speeds going up to 150 m/minute, the immediate rewinding of theprinted substrate is mandatory. The ink system must assure that there isno ink transfer from the freshly printed surface to the backside of theenrolled substrate which is in contact with it. In the case of webprinting machines equipped with hot air drying devices (as supplied e.g.from TEC-Systems, W. R. Grace & Co.), web printing speeds of up to 150m/min. have to be withstood, using engraving depths of up to 200microns. On sheet fed presses, 500 to 10,000 sheets, depending on theparticular printing substrate and on the depth of the engravings, mustbe stacked on piles right after printing, without interleaving sheets;

[0012] outstanding chemical and mechanical resistance of the printingaccording to specifications established by INTERPOL at the 5^(th)International Conference on Currency and Counterfeiting in 1969, or tothe Bureau of Engraving and Printing's test methods as stated inBEP-88-214 (TN) section M5;

[0013] acceptable toxicologic and environmental properties.

[0014] As it is known in the art of printing, the printed substrate mustgenerally be dried in order to allow subsequent processing, and toachieve the required resistance properties of the final product.

[0015] By the term “drying”, three different mechanisms are addressed,as it is well known to the man skilled in the art of printing. Two merephysical drying processes refer to the evaporation of volatile solventfrom the printed ink paste, leaving back its solid resin and pigmentcomponents, and to the resorption (sucking) of nonvolatile ink solventinto the substrate. A third, chemical drying process, also calledhardening or curing, refers to the transformation of a liquidcomposition into the solid state by a chemical polymerization orcross-linking reaction. One or more of these drying processes may beimplied in the drying of a same particular printing ink, and the printerdoes generally not make a difference between physical and chemicaldrying.

[0016] Intaglio inks are usually cured by an oxidation reaction. This isa rather slow drying method, and documents correspondingly printed andstacked as sheets cannot usually be handled for further processingbefore a drying time period of one to several days.

[0017] The curing of printed inks by UV radiation is known and widelyintroduced in the art of printing. UV curing allows a rapid, almostinstantaneous drying of the printed ink film, and hence opens the way toincrease production speed. The chemical curing reaction is in most casesinitiated by radicals, created by the UV irradiation. To obtainsufficient sensitivity to the UV radiation, it is necessary toincorporate a photoinitiator into the printing ink, said photoinitiatorbeing decomposed under the influence of the UV radiation, forming freeradicals, which in turn initiate the curing reaction.

[0018] FR 2274669 describes an intaglio printing ink based on a varnish(binder) based on tung oil and unsaturated aliphatic dicarboxylic acids,which can be cured by UV irradiation in the presence of oxygen. Due tothe type of chemical compounds used, the curing (polymerization) speedof this kind of binder is rather low, thus requiring a long period oftime to complete reaction. This intaglio ink is further described to bedispersible in caustic alkali solutions wherein the concentration of thecaustic alkali compound usually ranges from 0.5 to 2% by weight. Inorder to promote the dispersion in the wiping solution, surface tensionactive molecules (surfactants) like sulfonated castor oil or sodiumlaurylsulfate must be added.

[0019] EP 432093 describes another intaglio ink which is dispersible incaustic alkali solution. The concentration range of the caustic alkalisolution is the same as in the aforementioned patent. The said intaglioink cures upon UV irradation via a cationic polymerization process. Theproposed photoinitiators are representing toxicological hazards,however, as they contain toxic chemical elements such as As, Sb, or F,respectively.

[0020] It is an object of the present invention to overcome theshortcomings of the prior art; in particular by disclosing an intaglioink composition which can be easily and completely cured, which requiresless environmentally demanding compounds for the necessary post-wipingtreatment on the printing press, and which does not containtoxicologically problematic additives. A further property of thedisclosed intaglio ink is the water solubility of the ink and a simple,fast and economic way to precipitate the dissolved ink from the wipingsolution.

[0021] Another object of the present invention is to provide printinginks which are curable by UV—or by shortwave visible light radiation,for the printing of security documents by the engraved steel dieprinting method. Still another object of the invention is to provide aprinting ink which has improved water solubility, compared to the knownprinting inks. A further object of the invention is to provide aUV-curing printing ink based on photoinitiator compounds of lowtoxicity.

[0022] These and other objects are achieved by the invention inaccordance with the independent claims.

[0023] The printing ink of the present invention for the intaglioprinting process comprises a binder which is selected from the group ofwater-soluble or water-thinnable acrylate oligomers. In accordance withthe invention urethane acrylate oligomers and epoxy acrylate oligomersare the preferred oligomers, because these products are eithercommercially available or are easily prepared, starting from commercialproducts. Water-soluble urethane acrylates can be prepared fromwater-soluble or hydrophilic polyols (ethoxylated polyols such asethoxylated trimethylolpropane supplied from Perstorp SpecialityChemicals, Sweden) and 2-hydroxyethyl acrylate or ethoxylatedmonoacrylates (such as polyethylene or polypropylene glycolmonoacrylates, Bisomer, supplied by Laporte Performance Chemicals, UK)which are grafted to the water-soluble polyols using diisocyanates(toluene diisocyanate TDI, hexane-1,6 diisocyanate HDDI, isophoronediisocyanate IPDI, etc.).

[0024] Water-soluble epoxy acrylates can be prepared from ethoxylateddi- or triglycidyl ethers (such as polyethylene or polypropylene glycoldiglycidyl ethers, for example diethylene glycol diglycidyl ethersupplied by Sigma-Aldrich, polyoxypropylene di- and triglycidylethers,Eurepox supplied by Witco and for example the triglycidyl ether based on9-ethoxylated trimethylol propane, Grilonit V51-56, supplied by EMSChemie, Switzerland) by the addition of acrylic acid using a standardprocedure.

[0025] Alternative oligomers which can be used are polyester acrylatesand acrylic acrylates. Each oligomer comprises reactive acrylatefunctionalities and two or more repeating units separating thefunctional groups. The term “oligomer” is used to designate moleculeswhich are obtained by chemically linking together two or more reactiveunits (monomers), whereby the number of linked reactive units remainsstill relatively small. Oligomers are the intermediate stage between themonomers and the final polymer. They have a molecular weight which ishigher than the molecular weight of the monomers but lower than theM_(w) of the resulting final polymer. Acrylate monomers are moleculeswhich contain a reactive acrylate (R₁R₂C═CR₃—CO—OR₀) group (R₀ beingeither an organic residue, a hydrogen atom, or a negative charge).Acrylate oligomers are higher molecular weight products resulting of thecross-linking, via the acrylic double bond, of two or more acrylatemonomers.

[0026] Monomers, having low viscosity, are also described as reactivediluents, due to the fact that they are capable of reducing theviscosity of an oligomer or pre-polymer whilst being incorporated intothe structure of the cured final film. Binders or resins, which areessentially medium- to low-molecular weight polymers of synthetic ornatural origin, are used in inks and coating compositions to “glue”desired functional additives, such as pigments, to a substrate, and/orto produce a higher-molecular weight, cross-linked coating on thesurface of the substrate, which gives it desired properties andappearance.

[0027] Radiation curable oligomers or pre-polymers have much lowermolecular weight than resins. They consist of at most a few, repeatedmonomeric units, which, upon interaction with incident radiation ofsufficient energy, combine (“polymerize”) to give a cross-linked highmolecular weight structure. The terms “oligomer” and “pre-polymer” aregenerally used interchangeably in the technology field of radiationcurable coatings or inks, and are understood as being distinct from theterm “monomers”.

[0028] Strictly speaking, a monomer is a molecular species which is ableto form chemical links with the same or with similar types of molecules,resulting in chains, sheets or three-dimensional networks (polymers)which may comprise between a few up to a very large number of monomericbuilding blocks. In the context of the present invention, monomers areunderstood as molecular units which are polymerizable through theeffects of radiation, and which are generally, but not necessarily, oflower molecular weight than oligomers and prepolymers. Monomers havegenerally a lower viscosity than oligomers and can be used as reactivediluents to : decrease the viscosity of radiation curable formulations,improve the curing speed and increase the cross-link density (Chemistry& Technology of UV & EB formulation for coatings, inks and paints, vol.2, p. 31).

[0029] In the context of the present disclosure the term “watersolubility” means that an amount of 5 g of the compound referred to issoluble in 95 ml of the wiping solution at a temperature comprisedbetween 20° C. and 50° C. The corresponding cloud point temperatureshould be either below 20° C. or above 50° C. The usual wiping solutionsfor intaglio printing comprise caustic soda in a concentration range ofbetween 0.5 to 1.2%. For the intaglio inks of the present invention, thecaustic soda concentration is comprised in between 0% (pure water) and0.5%. The concentration of intaglio ink in the wiping solution does notexceed 5% in general. Water-soluble or water-thinnable acrylates of thepresent invention are selected as outlined above.

[0030] The group of urethane acrylates noteworthy comprises aliphaticurethane acrylates, aliphatic urethane diacrylates and urethane acrylateoligomers which are available from different suppliers. The group ofepoxy acrylates comprizes aliphatic epoxy acrylates, aliphatic epoxydiacrylates and epoxy acrylate oligomers, which are experimentalproducts available from Sicpa S. A. France, as described here above. Thebinder can also be a mixture of the aforementioned groups of acrylateoligomers. The use of water-soluble or water-thinnable compounds reducesthe amount of emulsifiers or surface tension active compounds needed toachieve a suitable dispersibility of the printing ink in aqueoussolutions.

[0031] Another, optional but preferred component of the printing inkcomposition are monomers selected from the group of water-soluble orwater-thinnable polyethyleneglycol (PEG) diacrylate or polyethoxylatedpolyol triacrylate monomers, and which are used to adjust the viscosityof the printing ink to the required value. The PEG diacrylate monomerscomprise compounds like PEG-X diacrylate monomers with X ranging from200 to 700, which are available from different suppliers. The(poly)ethoxylated polyol triacrylate monomers comprise compounds like7-ethoxylated trimethylolpropane triacrylate (TMPTA), 14-ethoxylatedTMPTA, 15-ethoxylated TMPTA, 20-ethoxylated TMPTA or 15-ethoxylatedbisphenol-A diacrylate monomers. Most of the compounds listed above arecommercially available. This list is not to be understood as beingcomplete and limiting the number of useful compounds in the mentionedclasses.

[0032] The viscosity of the ink composition depends among others of itsdetailed contents in water, pigments, fillers and other formulacomponents. However, there are limits as to the quantities of each ofthese substances in view of the printing process and the desiredproperties of the imprint. For example, in intaglio printing, an excessquantity of water in the ink is detrimental due to high pressure duringprinting.

[0033] A further component of the printing ink is the photoinitiatorwhich is needed to initiate the polymerization reaction of the describedbinder after irradiation by electromagnetic radiation or electron beamradiation.

[0034] Further components of the printing ink composition are additivessuch as pigments for providing the color of the ink, fillers,photosensitizers, photostabilizers, emulsifiers, as well as specialadditives for security purposes.

[0035] According to the invention the binder and optionally theadditional monomers have to be selected appropriately in order toproduce a composition which is substantially dispersible to 100% in awater wiping solution. A value of 100% being the optimum value. The term“dispersible” is to be understood as defined in Römpp Lexikon, “Lackeund Druckfarben”, published 1998, Thieme Verlag Stuttgart, page 147. Thewater wiping solution may contain sodium hydroxide in a concentrationrange between 0 and 0.5% by weight. The concentration of sodiumhydroxide is, however, preferably chosen between 0.1 and 0.3% and evenmore preferably between 0.1 and 0.2% by weight. A substantially fulldispersibility of the ink composition will avoid the separation of theink composition from the water wiping solution and thus avoid possibly aclogging of parts of the system containing the water wiping solution.Further, as it will be discussed below it allows to enhance therecovering of unused ink from the water wiping solution.

[0036] The low sodium hydroxide concentration of the wiping solutionrequired to print the ink of the present invention has the advantage ofcausing much less environmental charge, as compared to the wipingsolutions of much higher sodium hydroxide concentration required toprint the inks described in the prior art. The low-concentrated sodiumhydroxide solutions used to print the ink of the present invention do,however, still provide sufficiently alkaline conditions to efficientlycorrosion-protect the wiping system.

[0037] A major aspect of the invention concerns the adjustment andcontrol of the viscosity of the intaglio printing ink. The viscosity ofthe printing ink composition is chosen to be in between 7 and 60 Pa.s at40° C. A viscosity in between 12 and 40 Pa.s is preferable, and aviscosity of the composition between 15 and 30 Pa.s at 40° C. is evenmore preferable in order to achieve suitable rheological properties ofthe ink in the printing process.

[0038] As part of the invention the viscosity of the binder is selectedto lie in the range between 5 and 40 Pa.s at 40° C. This opens thepossibility to reduce the amount of further formula components forachieving the necessary rheological properties of the ink.

[0039] The binder is preferably selected from the aforementioned groupof compounds having a molecular weight M_(w) between 1,500 and 10,000g/mole, whereby the molecular weight M_(w) is determined according tothe procedures described in Polymer Synthesis, 2^(nd) revised edition byPaul Rempp and Edward W. Merrill, Ed. Hüthig & Wepf 1991, 344 pages.This range of molecular weights provides the ink with sufficient abilityfor crosslinking thoroughly and building a stable three dimensionalnetwork.

[0040] In the composition of the intaglio printing ink, the content ofwater-soluble or water-thinnable urethane acrylate or epoxy acrylateoligomers is comprised between 30 to 70% of the ink's total weight. Apreferable content of binder is in the range between 40 and 60%, andmore preferably between 45 and 55%, each referred to the total weight ofthe composition.

[0041] According to the invention, the content of water-soluble orwater-thinnable PEG diacrylate or polyethoxylated polyol triacrylatemonomers is preferably selected between 5 and 25% by weight, referred tothe total weight of the ink. A preferred content of water-soluble orwater-thinnable PEG diacrylate or polyethoxylated polyol triacrylatemonomers is between 10 and 20% by weight, and a content between 10 and15% by weight is even more preferred.

[0042] The amount of water-soluble or water-thinnable PEG diacrylate orpolyethoxylated polyol triacrylate or tetraacrylate monomers allows anadjustment of the viscosity of the total printing ink composition. Atthe same time these components provide similar functional groups asthose of the ink binder and participate thus in an optimal manner in theformation of the polymerized binder matrix.

[0043] The intaglio printing ink comprises a photoinitiator which iscapable of initiating a radical polymerization reaction within theaforementioned binder and monomers. The appropriate type of photoiniatorallows to start the appropriate type of polymerization reaction, whichideally proceeds with a high reaction rate and provides a rapid curingof the printed ink.

[0044] According to another aspect of the invention the photoinitiatorcan be selected from the group consisting of acetophenone orbenzophenone types of compounds. These types of photoinitiators are wellknown to break up into free radicals following irradiation with UV orshort-wavelength visible light, said radicals being capable ofinitiating the polymerization processes.

[0045] Additionally the photoinitiator may have a maximum absorption atwavelengths between 300 nm and 450 nm. Radiation of these wavelengths iseasily produced by devices such as a Hg medium pressure lamp, or aGa/Pb, Fe/Co doped Hg lamp, respectively.

[0046] Another aspect of the invention is in the use of aphotosensitizer, allowing for a higher yield of captured UV or shortwavevisible photons. The photosensitizer is selected from the thioxanthonegroup of chemical compounds. This group includes for exampleisopropyl-thioxanthone (ITX), 1-chloro-2-propoxy-thioxanthone (CPTX),2-chloro-thioxanthone (CTX) and 2,4-diethyl-thioxanthone (DETX), as wellas mixtures thereof.

[0047] According to a further aspect of the invention, an UV-stabilizeris added to the ink. In the inks of the present invention, FlorstabUV-1, supplied by Kromachem Ltd, UK, has been successfully used. Thepresence of the UV-stabilizer serves to avoid a premature polymerizationduring the preparation or during the handling of the ink prior to usesas well as on the printing press,.prior to the radiation-curing step.

[0048] Still another aspect of the invention concerns the pigmentcontent of the printing ink composition. According to the invention, aweight percentage of the pigment between 3 to 23% can be used. Preferredis a pigment content of between 5 to 12%, and even more preferably apigment content of between 7 to 10%, related to the total weight of theink. The type of pigment is selected from the group of pigments whichcan be applied in UV-curing inks according to the art.

[0049] According to a further aspect of the invention the filler contentof the composition is chosen to amount to between 6 and 50% by weight ofthe ink. The amount of filler lies preferably between 25 and 40% andmore preferably between 25 and 35%, referred to the total weight of theink.

[0050] Still according to another aspect of the invention, the filler isselected from the group of natural and artificially prepared calciumcarbonates. The type of calcium carbonate is preferably selected fromgrades which have a low oil absorption in order to avoid a trapping ofpart of the binder within the filler, which results in an incompletepolymerization of the binder.

[0051] A further part of the invention is a method for manufacturing anintaglio printing ink composition having a viscosity of between 7 and 60Pa.s at 40° C. A more preferred viscosity range is between 12 and 40Pa.s, and an even more preferred range is between 15 and 30 Pa.s at 40°C. The ink viscosity is adjusted according to the invention by addingwater-soluble or water-thinnable PEG diacrylate or polyethoxylatedpolyol triacrylate monomers.

[0052] A further part of the invention is a method of applying aradiation curing intaglio printing ink in an intaglio printing processusing a water wiping system. The water wiping system uses a wipingsolution having a sodium hydroxide concentration between 0 and 0.5% byweight, preferably between 0.1 and 0.3% and more preferably between 0.1and 0.2% by weight.

[0053] The ink waste dissolved in the wiping solution after the printingprocess can be precipitated by adding an inorganic metal halide orsulfate salt solution. This process is also called flocculation. Theeffect responsible for this change of solubility of the printing ink isthe so-called “salting out” which is well known in the field ofwater-soluble organic polymers. The addition of such inorganic saltsolution allows to recover a large amount of the printing ink dispersedin the waste wiping solution, and allows therefore to release a lesspolluted waste water. The precipitated ink can be recovered by standardsolid-liquid separation methods, such as filtration, ultra-filtration,centrifugation, etc., as known to the skilled in the art.

[0054] The remaining soluble organic contents of wiping solution afterthe ultrafiltration, floculation and filtration treatment can bedetermined with the help of Chemical Oxygen Demand (COD), Total OrganicCarbon (TOC) and Dissolved Organic Carbon (DOC) measurements which arestandard procedures in the field of waste-water characterization.Environment-friendly intaglio inks are characterized by low COD, TCO orDOC values of the residual wiping-solution waste.

[0055] The invention also includes a method for the precipitation of theaforementioned intaglio ink from a wiping solution of an intaglioprinting press. Said precipitation is noteworthy brought about by theaddition of an inorganic metal halide or sulfate salt solution such assolutions of calcium chloride, iron chloride, sodium chloride, potassiumchloride or aluminum sulfate.

[0056] The invention comprises further a method for precipitatingdispersed intaglio printing ink waste from a wiping solution, saidmethod including the adjustment of the temperature of the water wipingsolution to fall within a range of between 20 and 50° C., preferably ofin between 20 and 40° C., and more preferably of in between 25° and 35°C. The temperature noteworthy affects the solubility of the printing inkin the wiping solution.

[0057] In a further aspect the invention provides a method of making anintaglio printing on a substrate using the ink composition of theinvention. Said printing using said ink allows noteworthy a filmthickness of 20 to 60 microns, preferably of 30 to 50 microns, to bedeposited on paper or polymer substrates. A noteworthy advantage of theinks of the invention is that said rather high film thickness can becured thoroughly and rapidly by irradiation with electromagneticradiation or with electron beam radiation, providing an excellent andthoroughly dried imprint, having excellent chemical and physicalresistance, as well as tack-free printing surfaces immediately uponleaving the printing press.

[0058] The invention will now be explained further by non-limitingcomposition examples which are given for illustration purposes.

[0059] List of Abbreviations: Ebecryl 2001 UCB aliphatic urethanediacrylate oligomer Ebecryl 2002 UCB aliphatic urethane acrylateoligomer L300-627 SICPA France Urethane acrylate oligomer IRR 210 UCBalkoxylated triacrylate IRR 280 UCB PEG-400 diacrylate Photomer 4155Cognis 7-ethoxylated TMPTA Photomer 4158 Cognis 14-ethoxylated TMPTAOVP ® Optically Variable Pigment from Flex Corp., Santa Rosa. OVI ®Optically Variable Ink supplied by Sicpa S.A., Lausanne

EXAMPLE I

[0060] The inks have been prepared according to the general formula,printed and cured Samples A B Ebecryl 2002 46.6 L300-627 46.6 Wax(Montan) 4.0 4.0 Emulsifier 3.0 3.0 UV stabilizer 2.0 2.0 IRGALITE RED8B 8.0 8.0 Filler (CaCO₃) 30.0 30.0 ESACURE ITX 2.6 2.6 IRGACURE 369 3.83.8 Total 100.0 100.0

[0061] Results A B Viscosity/[Pa · s] 27 45 Tack/[T.U.] 240 300Wiping/paper* 5 5-6 Printing quality/[60° C.]* 5-6 5-6 Drying/[2 × 50m/min]* 3-4 3 Deterg. at 0.1% NaOH* 5-6 4-5 COD [mg O₂ · L⁻¹] 6′50010′800

[0062] The classification of the results of the wiping, printingquality, drying and detergibility in 0.1% NaOH solution is establishedaccording to laboratory experience.

EXAMPLE II

[0063] The inks have been prepared according to the procedure asdescribed for example I. Samples C D Ebecryl 2002 35.6 35.6 IRR 210 11.0IRR 280 11.0 Wax (Montan) 4.0 4.0 Emulsifier 3.0 3.0 UV stabilizer 2.02.0 IRGALITE RED 8B 8.0 8.0 Filler (CaCO₃) 30.0 30.0 ESACURE ITX 2.6 2.6IRGACURE 369 3.8 3.8 Total 100.0 100.0

[0064] Results C D Viscosity/[Pa · s] 16 20 Tack/[T.U.] 110 130Wiping/paper* 5-6 5-6 Printing quality/[60° C.]* 5-6 5-6 Drying/[2 × 50m/min]* 5 5 Deterg. at 0.1% NaOH* 5 5 COD [mg O₂ · L⁻¹] 10′675 10′865

EXAMPLE III

[0065] Samples E F Ebecryl 2001 32.0 Ebecryl 2002 35.6 Photomer 415514.6 Photomer 4158 11.0 Wax (Montan) 4.0 4.0 Emulsifier 3.0 3.0 UVstabilizer 2.0 2.0 IRGALITE RED 8B 8.0 8.0 Filler (CaCO₃) 30.0 30.0ESACURE ITX 2.6 2.6 IRGACURE 369 3.8 3.8 Total 100.0 100.0

[0066] Results E F Viscosity/[Pa · s] 27 14 Tack/[T.U.]* 225 125Wiping/paper* 5-6 5-6 Printing quality/[60° C.]* 5-6 5-6 Drying/[2 × 50m/min]* 5 5-6 Deterg. at 0.1% NaOH* 5 5 COD [mg O₂ · L⁻¹] 10′590 10′700

EXAMPLE IV

[0067] The following samples are disclosed with the use of a PEG400DA(IRR280 or Cray Valley SR344) monomer and an aliphatic urethane acrylateoligomer (Ebecryl 2002). Different examples have been prepared andtested including a red, a magnetic green and OVI® formulations Sample G:Red L300-600 35.6 IRR280 11.0 Wax (Montan) 4.0 Emulsifier 3.0 UVstabilizer 2.0 IRGALITE RED 8B 8.0 Filler (CaCO₃) 30.0 ESACURE ITX 2.6IRGACURE 369 3.8 Total 100.0 Sample H: Magnetic green Ebecryl 2002 46.6Wax (Montan) 4.0 Emulsifier 3.0 UV stabilizer 2.0 Mapico yellow 215 9.5IRGALITE GREEN GL 1.5 Carbon Black Raven 0.45 IRGALITE BLUE LGLD 0.35Filler (CaCO₃) 26.1 ESACURE ITX 2.6 IRGACURE 369 3.8 Total 100.0 SampleI: OVI ® green to blue Ebecryl 2002 46.6 Wax (Montan) 4.5 Emulsifier 3.0UV stabilizer 2.0 OVP Green/Blue 22.0 Filler (CaCO₃) 6.5 Aerosil 200 9.0ESACURE ITX 2.6 IRGACURE 369 3.8 Total 100.0

[0068] Results Sample G Sample H Sample I Viscosity/[Pa.s] 6-7 30-4030-40 Tack/[T.U.]* 100 200 240 Wiping/paper* 5-6 5-6 5-6 Printingquality/[60° C.]* 5* 5-6  5 Drying/[2 × 50 m/min]*  4-5* 4-5 5-6 Deterg.At 0.1% NaOH* 5* 5-6 5-6

EXAMPLE V

[0069] Sample J Ebecryl 2002 35.6 IRR280 11.0 Wax (Montan) 4.0Emulsifier 3.0 UV stabilizer 2.0 IRGALITE RED 8B 8.0 Filler (CaCO₃) 30.0ESACURE ITX 2.6 IRGACURE 369 3.8 Total 100.0

[0070] The ink of the above listed composition has been printed inindustrial printing conditions. The first printing trial was run withthe MiniOrlof Intaglio MOI printing press from De La Rue-Giori usingboth, a pure water wiping solution and a 0.1% NaOH wiping solution. Inboth conditions, printing quality and wiping were excellent. A secondprinting trial was run with the SuperOrlof Intaglio SOI printing pressin the same conditions. In the case of a pure water wiping solution, theink of example 1 was wiped off the plate and deterged from the wipingcylinder in a correct way. The wiping and deterging of the ink wassubstantially improved when using a 0.1 or 0.2% NaOH wiping solution. Atfurther increased NaOH concentration (0.3% NaOH and more), wiping anddeterging problems appeared again, which gradually worsened with furtherincreasing NaOH concentration.

[0071] COD values have been measured for Sample J in both situations:Sample J/CaCl₂ (35%) COD [mg O₂ · L⁻¹] Pure water solution pH = 6-72′750 0.2% NaOH, pH = 10-11 3′340

EXAMPLE VI

[0072] Sample K is like sample J but IRR280 is replaced by Ebecryl 2002.

[0073] COD of sample G has been measured. 3 g of fresh ink is dispersedfor 1-2 hours in 97 g of water (NaOH 0.1%) and heated at 50° C. The inkdispersion is allowed to cool under stirring. At 30° C., 1.5% of fossilmeal is added. A 10% CaCl₂ solution is added slowly in small portions(total 1.5 mL). Three different salt have been used to precipitate theink disclosed in sample G. The fluffy red precipitate is filtered offusing a paper filter. The solution is analysed in the same conditions.COD [mg O₂ · L⁻¹] Sample G Sample J Sample K NaCl 10% 10700 7530 5650CaCl₂ 10% 10600 7490 6490 FeCl₃ 10% 10670 7530 7600 Al₂(SO₄)₃ 10% 105707440 6940

[0074] As it can be seen from these results, COD values do not seem tobe related to the nature or the charge of the polyvalent cations usedfor flocculating the ink waste. The nature of the acrylate oligomers ormonomers is more critical, however.

1. An intaglio printing ink composition comprising (a) a first bindercompound selected from the group of water-soluble or water-thinnableacrylate oligomers; (b) optionally, a second monomeric binder compoundselected from the group comprising water-soluble or water-thinnable PEGdiacrylate or polyethoxylated polyol triacrylate monomers to adjustviscosity; (c) a photoinitiator to initiate polymerization of the binderupon irradiation by electromagnetic radiation or electron beamradiation; (d) optionally additives, preferably pigments, filler,photosensitizers, photostabilizers, emulsifiers, security pigments.wherein the first binder (a) and optionally the second binder (b) areselected to make the composition substantially fully dispersible in awater wiping solution having a sodium hydroxide concentration between 0and 0.5%, preferably between 0.1 and 0.3% and more preferably between0.1 and 0.2%.
 2. Intaglio printing ink according to claim 1 wherein thefirst binder component is a water-soluble or water-thinnable urethaneacrylate oligomer.
 3. Intaglio printing ink according to claim 1 whereinthe first binder component is a water-soluble or water-thinnable epoxyacrylate oligomer.
 4. Intaglio printing ink according to claim 1 whereinthe first binder component is a water-soluble or water-thinnable acrylicacrylate oligomer.
 5. Intaglio printing ink according to claim 1 whereinthe first binder component is a water-soluble or water-thinnablepolyester acrylate oligomer.
 6. Intaglio printing ink according to claim1 wherein the first binder component is a mixture of water-soluble orwater-thinnable oligomers according to claims 2 to
 5. 7. Intaglioprinting ink according to claims 1 to 6, wherein the viscosity of thecomposition is between 7 and 60 Pa.s, preferably between 12 and 40 Pa.s,and more preferably between 15 and 30 Pa.s at 40° C.
 8. Intaglioprinting ink according to claims 1 to 7 wherein the viscosity of thebinder (a) is between 5 and 40 Pa.s at 40° C.
 9. Intaglio printing inkaccording to one of the preceding claims wherein the molecular weightM_(w) of the binder (a) is between 1,500 and 10,000 g/mole.
 10. Intaglioprinting ink according to claims 1 to 7 characterized in that thecontent of water-soluble or water-thinnable acrylate oligomers iscomprised between 30 to 70% w, preferably between 40 and 60% w, and morepreferably between 45 and 55% w related to the total weight of the ink.11. Intaglio printing ink according to one of the claims 1 to 10characterized in that the content of water-soluble or water-thinnablePEG diacrylate or polyethoxylated-polyols triacrylate monomers isbetween 5 and 25% w, preferably between 10 and 20% w and more preferablybetweeen 10 and 15% w related to the total weight of the ink. 12.Intaglio printing ink according to the claims 1 to 11 characterized inthat the photoinitiator is capable of initiating radical polymerizationreactions of first binder (a) and second binder (b).
 13. Intaglioprinting ink according to claim 12 characterized in that the saidphotoinitiator is selected from the group consisting of acetophenone ofbenzophenone type compounds.
 14. Intaglio printing ink according toclaim 13 characterized in that the said photoinitiator has a maximumabsorption between 300 and 450 nm wavelength.
 15. Intaglio printing inkaccording to one of the claims 1 to 11 characterized in that thephotosensitizer is selected from the thioxanthone group of compounds,composed for example of isopropyl-thioxanthone (ITX),1-chloro-2-propoxy-thioxanthone (CPTX), 2-chloro-thioxanthone (CTX) and2,4-diethyl-thioxanthone (DETX) and mixtures thereof.
 16. Intaglioprinting ink according to one of the claims 1 to 15 characterized inthat an UV-stabilizer is added to prevent premature polymerization ofthe ink.
 17. Intaglio printing ink according to one of the claims 1 to16 characterized in that the pigment contents of the composition iscomprised between 3 to 15% w, preferably between 5 to 12% w and morepreferably 7 to 10% w related to the total weight of the ink. 18.Intaglio printing ink according to one of the claims 1 to 17characterized in that the filler content of the composition is comprisedbetween 20 and 50% w, preferably between 25 and 40% w and morepreferably between 25 and 35% w related to the total weight of the ink.19. Intaglio printing ink according to claim 18 characterized in thatthe filler is selected from the group comprising calcium carbonategrades having low oil absorption.
 20. A method for manufacturing anintaglio printing ink composition according to claim 1 to 19 wherein theviscosity of the composition is adjusted to have a value between 7 and60 Pa.s, preferably between 12 and 40 Pa.s, and more preferably between15 and 30 Pa.s at 40° C.; the viscosity adjustment comprising the stepof adding water-soluble or water-thinnable PEG diacrylate orpolyethoxylated polyol triacrylate monomers.
 21. Use of a compositionaccording to one or more of the claims 1 to 19 in an intaglio printingprocess comprising a wiping system including a water wiping solutionhaving a sodium hydroxide concentration between 0 and 0.5%, preferablybetween 0-1 and 0.3% and more preferably between 0.1 and 0.2%. 22.Method of applying a radiation curing intaglio printing ink compositionaccording to one or more of the claims 1 to 19 in an intaglio printingprocess comprising a wiping system, having a wiping solution with asodium hydroxide concentration between 0 and 0.5%, preferably between0.1 and 0.3% and more preferably between 0.1 and 0.2%, and wherein thewaste ink is separated from the wiping solution by adding an inorganicmetal halide or sulfate salt solution.
 23. Method of precipitating anintaglio ink according to claims 1 to 19 dispersed in a wiping solutionof an intaglio printing press by adding an inorganic metal halide orsulfate salt solution.
 24. Method of precipitating an intaglio inkaccording to claim 23 comprising the step of adjusting the temperatureof said wiping solution to a value between 20 and 50° C., preferablybetween 20 and 40° C. and more preferably between 25° and 35° C. 25.Method of making an intaglio imprint on a substrate using an intaglioprinting ink according to one of the claims 1 to 19, comprising thesteps of printing said ink in a film thickness of 20 to 60 microns,preferably 30 to 50 microns onto said substrate, and curing said imprintby irradiation with electromagnetic radiation or electron beamradiation.
 26. Security documents comprising an imprint made by anintaglio printing ink composition according to claims 1 to 19 and/or bya method for making an intaglio imprint according to claim 25.